Effects of Gas Adsorption Properties of an Au-Loaded Porous In₂O₃ Sensor on NO₂-Sensing Properties

Abstract

Gas adsorption properties of semiconductor-type gas sensors using porous (pr-) In₂O₃ powders loaded with and without 0.5 wt % Au (Au/pr-In₂O₃ and pr-In₂O₃ sensors, respectively) at 100 °C were examined by using diffuse reflectance infrared Fourier transform spectroscopy, and the effect of the Au loading onto pr-In₂O₃ on the NO₂-sensing properties were discussed in this study. We found the following: the resistance of the Au/pr-In₂O₃ sensor in dry air is lower than that of the pr-In₂O₃ sensor; the DRIFT spectra of both the sensors show a broad positive band between 1600 and 1000 cm^-1 in dry air (reference: in dry N₂ at 100 °C), which mainly originates from oxygen adsorbates and/or lattice oxygen, and that this band is much larger for the Au/pr-In₂O₃ sensor than for the pr-In₂O₃ sensor; the Au loading also increases the adsorption amount of H₂O and the reactivity of NO₂ on the pr-In₂O₃ surface; and the NO₂ response of the Au/pr-In₂O₃ sensor in dry air is marginally higher than that of the pr-In₂O₃ sensor in the examined concentration range of NO₂ (0.6-5 ppm) in dry air. The obtained results strongly support the enhancement of the NO₂ adsorption onto the pr-In₂O₃ surface by Au loading, which contributed to the improvement of the NO₂-sensing properties.